Rocket mods
Moderators: pompeiisneaks, Colossal
Rocket mods
I thought I'd share mods that I did to my Rocket. One of the issues a Rocket has is the pre-amp plate of the first triode operates at a relatively low voltage, this causes DC to get onto the grid and thus onto the volume pot resulting in a scratchy guitar pot when adjusting the volume. The fix is to either block the DC with a cap or to raise the DC voltage to the plate.
I also implemented Ken Fishers voicing mod. The voicing mod is fairly subtle, it is basically a slight mid cut which sound better for humbuckers.
This sort of thing has been discussed before but as there has been Rockets discussed lately, I thought I'd mention it.
I wanted to know the current through each EL-84 so I added 1 ohm 1% resistors to the circuit. I find them really handy knowing what each valve is doing.
Given that the cathode follower does operate under difficult circumstances. I decided to implement Merlin Blenecowes mod to prevent arc over which would damage an otherwise good valve.I also implemented Ken Fishers voicing mod. The voicing mod is fairly subtle, it is basically a slight mid cut which sound better for humbuckers.
This sort of thing has been discussed before but as there has been Rockets discussed lately, I thought I'd mention it.
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Yours Sincerely
Mark Abbott
Mark Abbott
Re: Rocket mods
Hi Mark. Good info.
My rocket also had low voltage at V1. Aaron (Xtian) helped me out with this, like the first picture ( scratchy pots)
Anyways thanks for the info
My rocket also had low voltage at V1. Aaron (Xtian) helped me out with this, like the first picture ( scratchy pots)
Anyways thanks for the info
Re: Rocket mods
The Marshall style power supply is the issue. The Vox AC-30 uses a parallel power supply which I assume is a bit noisier as it hasn't the series Pi filters the Marshall style power supply has, but the Vox power supply delivers higher voltages. The Dr Z version of the Rocket uses the Vox style power supply.
Yours Sincerely
Mark Abbott
Mark Abbott
Re: Rocket mods
The details in these pictures are great!
What is the purpose the diode/resistor on pins 3 and 4 of the third picture? I have not seen that before.
What is the purpose the diode/resistor on pins 3 and 4 of the third picture? I have not seen that before.
Re: Rocket mods
I got the mod from Merlin Blenecowe on his valve wizard site. About half way down the page it describes the purpose of the diode and resistor. It protects the cathode follower on start up. With the high cost of NOS and in my case ANOS valves, I didn't want to be going through 12AX7's. The beauty of the Rocket is you can even use valves like a 12AT7.
http://www.valvewizard.co.uk/dccf.html
http://www.valvewizard.co.uk/dccf.html
Yours Sincerely
Mark Abbott
Mark Abbott
Re: Rocket mods
Whats the voicing mod?
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Express, Comet 60, Jtm45, jtm50, jmp50, 6g6b, vibroverb, champster, alessandro rottweiler
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Express, Comet 60, Jtm45, jtm50, jmp50, 6g6b, vibroverb, champster, alessandro rottweiler
4x12" w/H75s
Re: Rocket mods
I saw the voicing mod in a real Rocket. Ken Fischer installed it. It puts a 22uF cap across the 1.5K (R5) and put a 220K resistor to ground to form a voltage divider with the 220K (R10) going to the P.I. stage.
https://ampgarage.com/forum/download/file.php?id=8003
https://ampgarage.com/forum/download/file.php?id=8003
Yours Sincerely
Mark Abbott
Mark Abbott
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Re: Rocket mods
Mark,
When I added a VVR to my Rocket/Z Wreck I had to install a cap to stop DC and scratchy volume control
I now have the rocket/Z Wreck differences on a switch so I can flip between them, one of them has more gain, I can't remember which though.
I use Russian Military EL84's and they've been very good.
M
When I added a VVR to my Rocket/Z Wreck I had to install a cap to stop DC and scratchy volume control
I now have the rocket/Z Wreck differences on a switch so I can flip between them, one of them has more gain, I can't remember which though.
I use Russian Military EL84's and they've been very good.
M
Re: Rocket mods
I'd like to see how you switch between a Z Wreck and a Rocket. I'm not sure which amp would have more gain. My Rocket does decent overdriven tones, but I really like it's clean tones best. It is quite a loud amp though, not a bedroom amp.
I have VVR to install in an amp, but I don't know which amp it would work best in. The Express was my first choice for VVR, but dropping pre-amp voltages effects the tone of the amp.
I have VVR to install in an amp, but I don't know which amp it would work best in. The Express was my first choice for VVR, but dropping pre-amp voltages effects the tone of the amp.
Yours Sincerely
Mark Abbott
Mark Abbott
Re: Rocket mods
I just added this voicing mod this evening and I think I will like having the option to change the character of the amp a little bit. I previously had the bypass cap on a switch so I just added the voltage divider to the same switch. I know there are a few more differences between the Rocket and Z-Wreck than just these two components but I think I will find it more useful than having just bypass cap switched as a boost.
I'm not sure if I can pick a favorite setting yet, I don't dislike either of them. My initial impression is the "Z" setting is a little tighter and might work better in the context of a band with 1 or two other guitar players/keys.
I should also note that I have a PPIMV in this amp and have only been able to play it at about 50%. I'm not sure yet how these different settings will sound at full volume.
I'm not sure if I can pick a favorite setting yet, I don't dislike either of them. My initial impression is the "Z" setting is a little tighter and might work better in the context of a band with 1 or two other guitar players/keys.
I should also note that I have a PPIMV in this amp and have only been able to play it at about 50%. I'm not sure yet how these different settings will sound at full volume.
Re: Rocket mods
The Zwreck has a different dropping string then the Rocket.
Early versions of the Zwreck also had lower filtering 8uf/450 B+1 and 2.
My Zwreck has a darker character to it which could be the Russian tubes and Edcor transformers.
Mark
Early versions of the Zwreck also had lower filtering 8uf/450 B+1 and 2.
My Zwreck has a darker character to it which could be the Russian tubes and Edcor transformers.
Mark
Re: Rocket mods
Though I would show pics of the finished amp. Still going strong and getting plenty of love.
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Yours Sincerely
Mark Abbott
Mark Abbott
Re: Rocket mods
That's a beauty, Mark. A very clean build. What speakers are you running in that 2x12 and open or closed?
Cheers
Cheers
Re: Rocket mods
Thanks for your kind words.
I’m still working out the speaker situation. I have been using my Marshall 18 watter as a speaker box. It has a Blue and a H30 in it.
In the pic the amp is sitting on a 2X12” cab with Mojotone Greyhounds in it. It’s Barry Marie’s cab and he finds they sound good with any amp.
I had heard good things about a Jensen Neo speaker, but I haven’t made any decisions yet.
https://ampgarage.com/forum/viewtopic.php?f=1&t=36198
Yours Sincerely
Mark Abbott
Mark Abbott
Re: Rocket mods
Beautiful amp, Mark!
Long ago I also adopted Merlin's cathode follower protection mod - use it on all my builds, and documented them here on AG.
I've also incorporated a series of different tone shaping mods, as I thin the Rocket really manages a pretty wide range of parameters well. Plenty of versatility available with the base circuit, and mods don't have to change the character of the amp too much if not desired.
I also had VVR on one Rocket that required the input cap. After removing the VVR I kept the cap - it does help.
Long ago I also adopted Merlin's cathode follower protection mod - use it on all my builds, and documented them here on AG.
I've also incorporated a series of different tone shaping mods, as I thin the Rocket really manages a pretty wide range of parameters well. Plenty of versatility available with the base circuit, and mods don't have to change the character of the amp too much if not desired.
I also had VVR on one Rocket that required the input cap. After removing the VVR I kept the cap - it does help.